makefiles/cflags.inc.mk: handle optional cflags

cpu/esp32/Makefile.include

@@ -105,6 +105,10 @@ CFLAGS  += -DLOG_TAG_IN_BRACKETS
 CFLAGS  += -Wno-unused-parameter -Wformat=0
 CFLAGS  += -mlongcalls -mtext-section-literals -fstrict-volatile-bitfields
 CFLAGS  += -fdata-sections -ffunction-sections -fzero-initialized-in-bss
+
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-overflow
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-truncation
+
 ASFLAGS += --longcalls --text-section-literals
 
 ifneq ($(CONFIGS),)

cpu/esp8266/Makefile.include

@@ -158,3 +158,7 @@ else
     FFLAGS += 0 $(FLASHFILE)-0x00000.bin
     FFLAGS += 0x10000 $(FLASHFILE)-0x10000.bin; esptool.py -p $(PORT) run
 endif
+
+OPTIONAL_CFLAGS_BLACKLIST += -fdiagnostics-color
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-overflow
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-truncation

makefiles/arch/atmega.inc.mk

@@ -50,3 +50,6 @@ ifeq ($(LTO),1)
   # See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=59396
   LINKFLAGS += -Wno-error
 endif
+
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-overflow
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-truncation

makefiles/arch/mips.inc.mk

@@ -66,3 +66,6 @@ export LINKFLAGS += $(MIPS_HAL_LDFLAGS)
 export LINKFLAGS += -L$(RIOTCPU)/$(CPU)/ldscripts
 export LINKFLAGS += $(CFLAGS_CPU) $(CFLAGS_DBG) $(CFLAGS_OPT)
 export LINKFLAGS += -Wl,--gc-sections
+
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-overflow
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-truncation

makefiles/arch/msp430.inc.mk

@@ -14,3 +14,7 @@ CFLAGS += $(CFLAGS_CPU) $(CFLAGS_LINK) $(CFLAGS_DBG) $(CFLAGS_OPT)
 ASFLAGS += $(CFLAGS_CPU) --defsym $(CPU_MODEL)=1 $(CFLAGS_DBG)
 # export linker flags
 export LINKFLAGS += $(CFLAGS_CPU) $(CFLAGS_DBG) $(CFLAGS_OPT) -Wl,--gc-sections -static -lgcc
+
+OPTIONAL_CFLAGS_BLACKLIST += -fdiagnostics-color
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-overflow
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-truncation

makefiles/cflags.inc.mk

@@ -11,37 +11,19 @@ endif
 # 0x0 might be a sane memory location for embedded systems, so the test must not be removed.
 # Right now clang does not use the *delete-null-pointer* optimization, and does not understand the parameter.
 # Related issues: #628, #664.
-ifeq ($(shell $(CC) -fno-delete-null-pointer-checks -E - 2>/dev/null >/dev/null </dev/null ; echo $$?),0)
-  ifeq ($(shell LANG=C $(CC) -fno-delete-null-pointer-checks -E - 2>&1 1>/dev/null </dev/null | grep warning: | grep -- -fno-delete-null-pointer-checks),)
-    CFLAGS += -fno-delete-null-pointer-checks
+OPTIONAL_CFLAGS += -fno-delete-null-pointer-checks
 
-    ifneq ($(shell $(CXX) -fno-delete-null-pointer-checks -E - 2>/dev/null >/dev/null </dev/null ; echo $$?),0)
-      CXXUWFLAGS += -fno-delete-null-pointer-checks
-    else
-      ifneq ($(shell LANG=C $(CXX) -fno-delete-null-pointer-checks -E - 2>&1 1>/dev/null </dev/null | grep warning: | grep -- -fno-delete-null-pointer-checks),)
-        CXXUWFLAGS += -fno-delete-null-pointer-checks
-      endif
-    endif
-  endif
-endif
-
-# Template for testing a compiler flag and adding it to CFLAGS (errors usually
-# happens when using older toolchains which do not support the given flags)
-define cflags_test_and_add
-  ifeq ($(shell $(CC) -Werror $(1) -E - 2>/dev/null >/dev/null </dev/null ; echo $$?),0)
-    CFLAGS += $(1)
-  endif
-endef
 # Use colored compiler output if the compiler supports this and if this is not
 # disabled by the user
 ifeq ($(CC_NOCOLOR),0)
-  $(eval $(call cflags_test_and_add,-fdiagnostics-color))
+  OPTIONAL_CFLAGS += -fdiagnostics-color
 endif
 
 # Fast-out on old style function definitions.
 # They cause unreadable error compiler errors on missing semicolons.
 # Worse yet they hide errors by accepting wildcard argument types.
-$(foreach flag,-Wstrict-prototypes -Wold-style-definition,$(eval $(call cflags_test_and_add,$(flag))))
+OPTIONAL_CFLAGS += -Wstrict-prototypes
+OPTIONAL_CFLAGS += -Wold-style-definition
 
 # Unwanted flags for c++
 CXXUWFLAGS += -std=%
@@ -59,7 +41,9 @@ CFLAGS += -fno-common
 # Enable all default warnings and all extra warnings
 CFLAGS += -Wall -Wextra
 # Enable additional checks for printf/scanf format strings
-$(foreach flag,-Wformat=2 -Wformat-overflow -Wformat-truncation,$(eval $(call cflags_test_and_add,$(flag))))
+OPTIONAL_CFLAGS += -Wformat=2
+OPTIONAL_CFLAGS += -Wformat-overflow
+OPTIONAL_CFLAGS += -Wformat-truncation
 
 # Warn if a user-supplied include directory does not exist.
 CFLAGS += -Wmissing-include-dirs
@@ -70,6 +54,9 @@ ifeq (,$(filter -DDEVELHELP,$(CFLAGS)))
   endif
 endif
 
+# Add the optional flags that are not architecture/toolchain blacklisted
+CFLAGS += $(filter-out $(OPTIONAL_CFLAGS_BLACKLIST),$(OPTIONAL_CFLAGS))
+
 # Default ARFLAGS for platforms which do not specify it.
 # Note: make by default provides ARFLAGS=rv which we want to override
 ifeq ($(origin ARFLAGS),default)

makefiles/toolchain/llvm.inc.mk

@@ -71,3 +71,7 @@ ifneq (,$(TARGET_ARCH))
   INCLUDES    += $(GCC_C_INCLUDES)
   CXXINCLUDES += $(GCC_CXX_INCLUDES)
 endif
+
+OPTIONAL_CFLAGS_BLACKLIST += -fno-delete-null-pointer-checks
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-overflow
+OPTIONAL_CFLAGS_BLACKLIST += -Wformat-truncation